Non-crimping polyester monofilament and process for producing same

ABSTRACT

A non-crimping polyester monofilament having an excellent resistance to abrasion and satisfactory mechanical strength and modulus has a intrinsic viscosity distribution such that the farther the location of a part of the monofilament from the longitudinal axis of the monofilament, the lower the intrinsic viscosity of a portion of polyester resin located in the part of the monofilament, wherein a peripheral part of the monofilament formed from a portion of the polyester resin having a lowest average intrinsic viscosity of 0.6 to 1.1 and concentrically surrounds a center part of the monofilament formed from another portion of the polyester resin having a highest average intrinsic viscosity, and the intrinsic viscosities the polyester resin portions for the peripheral and center parts of the monofilament is controlled by controlling the heat history of each of the portions of the polyester resin in a melt spinneret for producing the monofilament.

TECHNICAL FIELD

The present invention relates to a non-crimping polyester monofilamentand a process for producing the same. More particularly, the presentinvention relates to a non-crimping polyester monofilament having animproved surface property and usable as a material monofilament, forropes, nets, artificial gut, tarpaulins, tents, screens, paragliders andsailcloths, particularly for producing mesh woven fabrics forscreen-printing, especially high-mesh high-modulus plain gauzes forscreen printing which are required to have a high accuracy, in theproduction of base plates for printed circuits.

BACKGROUND ART

Polyester monofilaments, which may be referred to “monofilaments” or“material yarns”, are widely employed not only in the clothing field butalso in the industrial material field. Particularly, in the industrialmaterial field, the polyester monofilaments are used as material yarnsfor tire cords, ropes, nets, gut, tarpaulins, tents, screens,paragliders, and sailcloths. The monofilaments for the industrialmaterial use must satisfy severe requirements in adhesive property torubber, fatigue resistance, dyeability, wear resistance and knotstrength.

The requirements in physical properties for the monofilaments has becomemore and more severe and improvements in rubber-adhesion, fatigueresistance, dyeing property, wear resistance and knot strength of themonofilaments is strongly required.

Particularly, the polyester monofilaments have excellent dimensionalstability and thus, in the field of the material yarns for plain gauzesfor screen printing, the polyester monofilaments now replace the naturalfilaments, for example, silk filaments and inorganic filaments, forexample, stainless steel filaments.

In the field of the circuit printing for electronic devices, forexample, base plates of printed circuits, the degree of integration ofthe printed circuits is further increased, and thus the accuracy of thecircuit printing by the screen printing is strongly required to beincreased. Namely, the printing screen for the circuit printing isrequired to has further increased mesh degree, mechanical strength andmodulus. Therefore, the material yarns for the printing screen arerequired to have further enhanced mechanical strength and modulus and afurther decreased thickness. Generally, it is well known that, toincrease the mechanical strength and the modulus of the polyestermonofilaments, melt-spun, undrawn polyester monofilament is heat-drawnat a high draw ratio to orientate and crystallize the polyestermolecules in the monofilament to a great extent.

However, in the procedure for producing the printing screen, thepolyester monofilaments are woven into a high density woven fabric tomeet with the above-mentioned requirement of a high mesh fabric. In thisweaving procedure, the polyester monofilaments are subjected to repeatedsevere abrasions with a reed of the weaving machine (loom).

Therefore, a portion of the periphery of the monofilament is worn outand fluff or powder-like scum is generated in the weaving machine. Thusthe productivity of the printing screen is decreased and the quality ofthe product is degraded. Also, it is known that the higher theorientation degree and the crystallization degree of the polyestermonofilament, the severer the above-mentioned problems in the weavingprocedure. When the scums are accumulated in the weaving machine, theweaving procedure is stopped, and when woven printing screen iscontaminated with the scum, the contaminating scum causes printingdefects to be generated on the printed products in a precision printingprocedure.

To prevent or restrict the generation of the scum in the weavingprocedure, for example, Japanese Unexamined Patent Publication No.55-16,948 proposes to employ, as warp yarns, stretch polyester filamentyarns having an ultimate elongation of 30 to 60%. However, the highstretch yarns usually have a low modulus and thus cannot meet therequirement of high-strength and high-modulus for the material yarns forthe printing screens.

As mentioned above, a high draw ratio is necessary to obtain thehigh-strength high-modulus polyester monofilament. However, the highdraw ratio causes a portion of the polyester resin located in aperipheral part of the resultant drawn polyester monofilament to have ahigher degree of orientation of the polyester molecules than that ofanother portion of the polyester resin located in a center part of themonofilament, and thus the peripheral part of the monofilament is easilypartially worn out by abrasion. To solve this problem, there are variousproportions of forming the peripheral part of the monofilament by apolymeric melt different from conventional one, to realize both theproduction of high strength high modulus monofilament and the preventionof scum generation during the weaving prodcedure.

For example, Japanese Unexamined Patent Publication No. 1-132,829discloses a core-in-sheath type monofilament comprising a core partformed from a polyester and a sheath part formed from a nylon. Thiscore-in-sheath type monofilament has a high mechanical strength andexhibits a high restriction effect on scum generation. However, in thistype of monofilament, the sheath part exhibits a high moistureabsorption due to the coherent property of nylon and this high moistureabsorption of the sheath portion disadvantageously causes themonofilament to exhibit, as a whole, a reduced dimensional stability.Further, since the monofilament is constituted from a polyester sheathpart and a nylon core part and polyester and nylon are uncompatible witheach other, when the monofilament is repeatedly fatigued under stressduring printing procedures the polyester sheath part and the nylon corepart may easily separate, at the interface therebetween, from eachother.

To solve the above-mentioned problem, Japanese Unexamined PatentPublication No. 2-289,120 provides a core-in-sheath type monofilamenthaving a core part formed from a polyester homopolymer having anintrinsic viscosity of 0.80 and a sheath part formed from a polyethyleneglycol-copolymerized polyester having an intrinsic viscosity of 0.67. Inthe core-in-sheath type composite monofilament, the wearing out of themonofilament due to contact and friction with reed and heald of aweaving machine occurs at the peripheral part of the monofilament.Therefore, the above-mentioned core-in-sheath type monofilament ischaracterized in that the peripheral part of the monofilament is formedfrom a polyester copolymer having a low glass transition temperature andexhibiting high resistance to friction and abrasion. Therefore, thestrength and modulus of the core-in-sheath type monofilament dependmainly on those of the core part formed from the polyester homopolymer.Thus, in view point of the mechanical properties of the monofilament, itis advantageous that the sheath part formed from the polyester copolymerhas a small thickness, in other words, in the cross-section of themonofilament, the ratio of the cross-sectional area of the sheath partto the total cross-sectional area of the monofilament is kept low.However, when the thickness of the sheath part of the monofilament istoo low, the core part of the monofilament may be partially exposed tothe outside and, simultaneously, since the compatibility of thepolyester copolymer for the sheath part with the polyester homopolymerfor the core part is low, separation of the sheath part from the corepart at the interface therebetween unavoidably occurs. This phenomenoncauses the scum-restriction effect of the monofilament and the physicalproperties and functions of the monofilament to be degraded.

For example, in core-in-sheath type monofilaments for plain gauze forprinting screen available in the trade in 1998, the cross-sectionalproportion of the sheath part is 30 to 40% which is higher than therange proposed in the above-mentioned Japanese unexamined patentpublication.

DISCLOSURE OF THE INVENTION

An object of the present invention is to provide a non-crimpingpolyester monofilament having a high mechanical strength, a high modulusand a high resistance of a peripheral part thereof to abrasion andcapable of having a small thickness, and a process for producing thesame with a high efficiency.

Another object of the present invention is to provide a non-crimpingpolyester monofilament having a high resistance of a peripheral partthereof to abrasion in a weaving procedure, useful for producing plainguaze for precision printing screen having a high mesh, a highmechanical strength and a high modulus, and capable of being formed witha very small thickness, and a process for producing the same with a highefficiency.

The above-mentioned object can be attained by the polyester monofilamentof the present invention and the process of the present invention forproducing the same.

The non-crimping polyester monofilament of the present invention isformed from a polyester resin, and in the monofilament, the polyesterresin has an intrinsic viscosity which varies in distribution in such amanner that the farther the location of a part of the monofilament fromthe longitudinal axis of the monofilament in the direction at rightangles to the longitudinal axis, the lower the intrinsic viscosity of aportion of the polyester resin located in the part of the monofilament,and a portion of the polyester resin located in a peripheral part (p) ofthe monofilament has an average intrinsic viscosity [η]f−p of 0.6 to1.1, determined in orthochlorophenol at a temperature of 35° C., theperipheral part (p) concentrically surrounding a center part (c) of themonofilament extending along the longitudinal axis of the monofilament.

The process of the present invention for producing a non-crimpingpolyester monofilament, comprises:

melting a polyester resin having an intrinsic viscosity of 0.8 to 1.3,determined in o-chlorophenol at a temperature of 35° C.;

dividing the polyester resin melt into at least two portions;

passing the polyester resin melt portions through at least two passageswhich cause the intrinsic viscosity of the polyester resin melt portionsto be decreased to extents different from each other;

extruding the polyester resin melt portions which are different, fromeach other, in the intrinsic viscosities thereof, through amelt-spinning orifice, in such a manner that a polyester resin meltportion having a highest intrinsic viscosity is extruded through acenter part of the orifice, and a polyester resin melt portion having alowest intrinsic viscosity is extruded through a peripheral partconcentrically surrounding the center part of the orifice, to form afilamentary stream of the polyester resin melt;

drafting and solidifying the resultant filamentary stream of thepolyester resin melt to form a monofilament of the polyester resin;

taking up the drafted and solidified polyester monofilament; and

heat-drawing the taken-up undrawn monofilament,

wherein during the extruding step through the heat-drawing step, thepolyester resin portions different in intrinsic viscosity from eachother are diffused, at the interface portion thereof, into each other,to cause the resultant monofilament to have a distribution of theintrinsic viscosity of the polyester resin such that the farther thelocation of a part of the monofilament from the longitudinal axis of themonofilament in the direction at right angles to the longitudinal axis,the lower the intrinsic viscosity of a portion of the polyester resinlocated in the part of the monofilament, and a portion of the polyesterresin located in the peripheral part of the monofilament has an averageintrinsic viscosity [η]f−p of 0.6 to 1.1 determined in o-chlorophenol ata temperature of 35° C.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic explanatory view of a polyester monofilament ofthe present invention having a center part (c) and a peripheral part (p)concentrically surrounding the center part (c),

FIG. 2 is an explanatory diagram showing relationships S1, S2 and S3between a distance (X) from a longitudinal axis of the monofilamentshown in FIG. 1 and an intrinsic viscosity [η]f of a polyester resinfrom which the monofilament is formed.

FIG. 3(a) is an explanatory vertical cross-sectional view of anembodiment of the melt-spinneret for producing the polyestermonofilament of the present invention,

FIG. 3(b) is an explanatory horizontal cross-sectional view of themelt-spinneret of FIG. 3(a) along a horizontal line A—A,

FIG. 4 is an explanatory vertical cross-sectional view of anotherembodiment of the melt-spinneret for producing the polyestermonofilament of the present invention.

BEST MODE OF CARRYING OUT THE INVENTION

In the present invention, a non-crimping polyester monofilament having ahigh resistance, at a peripheral part thereof, to abrasion andsatisfactory mechanical strength and modulus can be obtained byutilizing a reduction in intrinsic viscosity of the polyester resin suchthat when a melt of a polyester resin is fed into a melt-spinneret,passed through the spinneret and extruded from the spinneret, theintrinsic viscosity of the polyester resin melt is reduced in responseto heat history of the polyester resin melt passed in the spinneret,namely the higher the temperature of the spinneret and the longer thestaying time of the polyester resin melt in the spinneret, the largerthe reduction in the intrinsic viscosity of the polyester resin melt.

The polyester monofilament of the present invention has an improvedsurface (periphery) property. Namely, in the polyester monofilament ofthe present invention, the peripheral part thereof exhibits improvedproperties, for example, abrasion resistance to metallic materials, forexample, reed, roller and yarn guide of weaving machine, adhesiveproperty to rubber, fatigue resistance, dyeing property, abrasionresistance and knot resistance, in comparison with those of the centerpart of the monofilament.

The polyester monofilament of the present invention preferably has anaverage stress of 29.4 mN or more per 0.9 dtex (3 g/denier or more)under an elongation of 5%, an average tensile strenght of 58.4 mN ormore per 0.9 dtex and an average ultimate elongation of 10 to 30%, whichare satisfactory for practical use of the polyester monofilament.

In the production of a polyester multifilament, a melt of polyesterresin is passed through a filtering layer arranged immediately above amelt spinneret having a plurality of melt-spinning orifices under a highpressure. In this filtering procedure, a portion of the polyester resinmelt passed through a center part of the filtering layer and anotherportion of the melt passed through an outer portion of the filteringlayer are different in staying time, from the filtering layer to thespinning orifice, from each other. Namely, the portion of the meltpassed through the outer portion of the filtering layer has a longerstaying time than that of the portion of the melt passed through thecenter part, and thus is heat-decomposed to a higher extent and has alower intrinsic viscosity than that of the portion of the melt passedthrough the center part of the filtering layer.

When the polyester resin melt is extruded through the plurality oforifices, the filaments formed from the polyester resin melt portionpassed through the center part of the filtering layer have a higherintrinsic viscosity, and other filaments formed from the polyester resinmelt portion passed through the outer part of the filtering layer have alower intrinsic viscosity. Thus, the resultant multifilaments are unevenin the physical properties thereof.

Many attempts have been made to make the intrinsic viscosity of thepolyester resin melt portions located immediately upstream to thespinning orifices even. For example, in one attempt, a rectificationplate or a static mixer is arranged immediately below the filteringlayer to uniformly knead-mix the filtered melt portions of the polyesterresin and to introduce a polyester resin melt having uniform intrinsicviscosity to the melt-spinning orifices for the multifilaments.

In the present invention, contrary to the above-mentioned prior art, themelt portions of a polyester resin different in intrinsic viscosity fromeach other are utilized to produce a non-crimping polyester monofilamenthaving a desired surface property, without uniformalizing them. Namely,in the present invention, a center part of the monofilament is formedfrom a portion of the polyester resin melt having a highest intrinsicviscosity, a peripheral portion of the monofilament is formed fromanother portion of the polyester resin melt having a lowest intrinsicviscosity, and optionally an intermediate part between the center partand the peripheral part of the monofilament is formed from still anotherportion of the polyester resin melt having an intermediate intrinsicviscosity between the highest and the lowest intrinsic viscosities.

In the polyester monofilament of the present invention, the intrinsicviscosity of the polyester resin varies in such a manner that thefarther the location of a part of the monofilament from the longitudinalaxis of the monofilament in the direction at right angles to thelongitudinal axis, the lower the intrinsic viscosity of a portion of thepolyester resin located in the part of the monofilament. In other words,the intrinsic viscosity of the polyester resin decreases with anincrease in a distance from the longitudinal axis of the monofilamentmeasured in the direction at right angles to the longitudinal axis.

In the polyester monofilament of the present invention, the peripheralpart concentrically surrounds the center part of the monofilamentextending along the longitudinal axis, and thus the resultantmonofilament of the present invention has no self-crimping property.

The peripheral part of the monofilament of the present invention has anaverage intrinsic viscosity [η]f−p of 0.6 to 1.1, preferably 0.6 to 0.9,determined in orthochlorophenol at a temperature of 35° C.

In our research, it was confirmed that with respect to a polyestermonofilament having an average intrinsic viscosity [η]f−a of thepolyester resin of 0.65 to 0.85, an ultimate elongation of 20 to 40%, atensile strength of 58.8 to 83.4 mN per 0.9 dtex (1.0 denier) (6.0 to8.5 g/denier), provided that the monofilaments were produced under thesame production conditions, a reduction of the intrinsic viscosity ofthe polyester resin is in an extent of 0.01, causes the tensile strengthof the resultant polyester monofilaments to decrease in an extent ofabout 1.96 mN per 0.9 dtex (about 0.2 g/denier), and the ultimateelongation of the resultant polyester monofilaments to increase in anextent of about 1.5%. From this fact, it was expected that when, in aproduction of a polyester monofilament, a center part of a monofilamentis formed from a portion of a polyester resin melt which had a lowreduction in intrinsic viscosity generated during a melt spinningprocedure and a peripheral part of the monofilament is formed from aportion of a polyester resin melt which had a high reduction inintrinsic viscosity generated during the melt spinning procedure, theresultant polyester monofilament has a peripheral part thereof having ahigh ultimate elongation and a low modulus in comparison with those ofother parts of the monofilaments, and a center part of the monofilamenthaving a satisfactory mechanical strength and modulus.

The present invention will be further explained by referring to thedrawings.

FIG. 1 is a schematic explanatory view of a polyester monofilament ofthe present invention having a circular cross-sectional profile. In FIG.1, a polyester monofilament 1 extends along a longitudinal axis 1 athereof and has a center part 1 c surrounding the longitudinal axis 1 aand a peripheral part 1 p concentrically surrounding the center part 1c. In a cross-section of the monofilament 1, the monofilament 1 has aradius R, the radius of the center part 1 c is represented by Lc and thethickness of the peripheral part 1 p determined along the radium R ofthe monofilament 1 is represented by Lp. Namely Lc+Lp=R. Since, thecenter part 1 c and the peripheral part 1 p are in a concentricrelationship with each other, the monofilament exhibits, as a whole, anon-crimping property.

Referring to FIG. 2 which is an explanatory diagram showingrelationships S1, S2 and S3 between the distance (X) from a longitudinalaxis of the monofilament shown in FIG. 1 and an intrinsic viscosity (Y)of a polyester resin from which the monofilament is formed. In straightlinear relationship S1, the intrinsic viscosity ([η]f) simply decreasesalong a straight line Y₁-Y₂ inclined downward from Y₁ to Y₂. In thiscase, the intrinsic viscosity of the polyester resin in the monofilamentproportionally decreases with an increase in distance from thelongitudinal axis of the monofilament determined at right angles to thelongitudinal axis. In stepwise relationship S2, the intrinsic viscosityof the polyester resin in the monofilament decreases stepwise at theinterface between the center part 1 c and the peripheral part 1 p of themonofilament. Namely, the intrinsic viscosity of a portion of thepolyester resin located in the center part 1 c of the monofilament iseven at a level Y′₁ and is higher than the intrinsic viscosity ofanother portion of the polyester resin located in the peripheral part 1p of the monofilament which viscosity is even at a level Y′₂. Inrelationship S3, the intrinsic viscosities of the polyester resin in thecenter and peripheral parts of the polyester continuously decreasedownward from Y″₁ to Y″₂ along a curve of secondary degree. In S3, theportion of the polyester resin having a highest intrinsic viscosity forthe center part and the portion of the polyester resin having a lowestintrinsic viscosity for the peripheral part are diffuse-mixed at theinterface part between the center and peripheral parts with each other.In the present invention, the intrinsic viscosities of the portions ofpolyester resin located in the center and peripheral parts of themonofilament are represented by average intrinsic viscosities [η]f−c and[η]f−p, respectively.

Compared with the monofilament of the present invention, theconventional polyester monofilament of, for example, Japanese UnexaminedPatent Publication No. 2-289,120 is constituted by a core part formedfrom a polyester homopolymer having an intrinsic viscosity of 0.80 and asheath part formed from a polyethyleneglycol-copolymerized polyestercopolymer having an intrinsic viscosity of 0.67 and exhibiting a lowcompatibility with the polyester homopolymer. In the conventionalmonofilament, the distribution of intrinsic viscosity of the polymers isin the manner shown in the relationship S2 of FIG. 2, wherein theintrinsic viscosity decreases stepwise at the interface between the coreand sheath parts of the monofilament. The resultant polyestermonofilament of the present invention has the peripheral part thereofhaving an improved surface property, namely a high resistance toabrasion and exhibit satisfactory mechanical strength and modulus.

For the purpose of improvement of the surface property of the polyestermonofilament, it is important that the average intrinsic viscosity ofthe peripheral part of the monofilament is controlled to a range of from0.6 to 11, preferably 0.6 to 1.0, particularly 0.6 to 0.8 when themonofilament is used for a plain guaze for a printing screen. When theabove-mentioned feature is attained, the abrasion resistance of theresultant monofilament against metals, for example, metallic reeds,rollers and yarn guides, is significantly enhanced, and the mechanicalstrength of the resultant monofilament is substantially not affected bythe above-mentioned feature.

In an embodiment of the polyester monofilament of the present invention,the center part (c) extending along a longitudinal axis of themonofilament has the highest average intrinsic viscosity and isconcentrically surrounded by the peripheral part (p) of themonofilament.

In another embodiment of the polyester monofilament of the presentinvention, the center part (c) extending along a longitudinal axis ofthe monofilament has a highest average intrinsic viscosity and isconcentrically surrounded by an intermediate part (i) and the peripheralpart (p) of the monofilament concentrically surrounds the intermediatepart (i) of the monofilament, the portion of the polyester resin locatedin the intermediate portion of the monofilament having an intrinsicviscosity lower than that of the center part (c) but higher than that ofthe peripheral part (p).

The portions of the polyester resin for the center, peripheral andoptionally intermediate parts of the monofilament are preferably thesame in the type of polymer as each other and are different in intrinsicviscosity from each other.

The polyester resin preferably comprises at least one member selectedfrom the group consisting of polyethylene terephthalate, polybutyleneterephthalate, polyethylene naphthalate, and polytrimethyleneterephthalate.

In the present invention, it is essential that the monofilament isformed from a single type of a polyester resin, for example,polyethylene terephthalate, polybutylene terephthalate or polyethylenenaphthalate, while the intrinsic viscosities of portions of thepolyester resin for forming the center part, peripheral parts andoptionally intermediate parts are varied from each other by impartingheat-histories different from each other to the portions of thepolyester resin for forming the parts of the monofilament.

In the present invention, a non-crimping, core-in-sheath type polyestermonofilament can be formed from at least two types of polyester resinsdifferent in intrinsic viscosity from each other by a conjugatemelt-spinning process in which a melt of polyester resin having a higherintrinsic viscosity is extruded through a center part of a melt-spinningorifice and another melt of polyester resin having a lower intrinsicviscosity is extruded through a peripheral part of the orifice, while anintrinsic viscosity gradient decreasing from the core part toward theperiphery of the monofilament is imparted to the polyester resin meltfor the peripheral part of the monofilament. Of course, the sameintrinsic viscosity gradient as mentioned above may be imparted to thehigher intrinsic viscosity polyester resin melt for the core part of themonofilament. However, the intrinsic viscosity gradient of the centerpart of the monofilament is not so important in imparting a highmechanical strength and modulus to the monofilament.

In the production of a polyester monofilament from two differentpolyester resins by using a melt spinneret similar to FIGS. 3(a) and(b), when a polyester resin melt stream introduced into a passage 5 andanother polyester resin melt stream introduced into a passage 7 throughpassages 6 are separately controlled, the resultant monofilament has acore part having an even distribution of intrinsic viscosity and asheath part having an intrinsic viscosity gradient decreasing in thedirection from the core part toward the periphery of the monofilament.

The polyester resin for the polyester monofilament preferably has, as awhole, an average intrinsic viscosity [η]f−a of 0.65 to 1.2, morepreferably 0.7 to 1.1, determined as mentioned above.

Also, in the polyester monofilament of the present invention, a portionof the polyester resin located in the center part (c) of themonofilament preferably has an average intrinsic viscosity [η]f−c of 0.7to 1.3, more preferably 0.75 to 1.2, determined as mentioned above, buthigher than the average intrinsic viscosity [η]f−p of the portion of thepolyester resin located in the peripheral part of the monofilament. Theabove-mentioned features contribute to enabling the resultant polyestermonofilament to exhibit a satisfactory mechanical strength and mululus.

In the polyester monofilament of the present invention, preferably theaverage intrinsic viscosity [η]f−c of the portion of the polyester resinlocated in the center part (c) of the monofilament is 0.02 to 0.20 morepreferably 0.04 to 0.15, above the average intrinsic viscosity [η]f−p ofthe portion of the polyester resin located in the peripheral part (p) ofthe monofilament.

In the cross-section of the polyester monofilament of the presentinvention, preferably, the area of the center part (c) of themonofilament is in a proportion of 0.6 to 0.95, more preferably 0.80 to0.95, to the whole cross-sectional area of the monofilament, and thusthe area of the peripheral part (c) of the monofilament is in aproportion of 0.05 to 0.4, more preferably 0.05 to 0.2, to the wholecross-sectional area of the monofilament.

When the polyester monofilament of the present invention has a circularcross-sectional profile as shown in FIG. 1, preferably, the ratio (Lc/R)of the radium Lc of the circular center part C to the radius R of thecross-section is 0.77 to 0.98, more preferably 0.89 to 0.98, and thusthe ratio (Lp/R) of the thickness Lp (=R−La) of the peripheral part p inthe form of a ring concentrically surrounding the circular center part Cto the radius R of the cross-section is 0.02 to 0.23, more preferably0.02 to 0.11.

As mentioned above, the intrinsic viscosity of the polyester resin inthe monofilament has a gradient distribution such that the intrinsicviscosity decreases in the direction of from the longitudinal axistoward the periphery of the monofilament. The average gradient (α) ofthe polyester resin from which the monofilament is formed is preferably1 to 30, more preferably 2 to 27. In FIG. 2, the average ingredient (α)shown in S1 calculated by dividing the distance between Y₁ and Y₂ with aradius R of the cross-section, namely α=({overscore (Y₁+L −Y₂+L )}/R).Also, in S3, the average gradient α=({overscore (Y″₁+L −Y″₂+L )})/R.

The polyester monofilament preferably has a high longitudinal uniformityin the thickness thereof. The longitudinal uniformity of the thicknessis usually represented by an evenness (U %) in thickness. Preferably,the polyester filament of the present invention has a thickness evenness(U %) of 1.5% or less, more preferably 0.8% or less.

Also, the non-crimping property of filaments or fibers can berepresented by a total percentage crimp (TC). The non-crimping polyestermonofilament of the present invention preferably has a TC of 1.5% orless, more preferably 1.0% or less.

The polyester monofilament of the present invention is useful forvarious industries and preferably has a thickness of 1.1 to 55.6 dtex (1to 55 denier), more preferably 3.3 to 33.3 dtex (3 to 30 denier). Itshould be noted that in the present invention, very thin polyestermonofilaments having a thickness of 1.1 to 11.1 dtex (1 to 10 denier)can be practically produced and employed.

The polyester monofilament of the present invention can be produced bythe process comprising the steps of:

melting a polyester resin having an intrinsic viscosity of 0.8 to 1.3,determined in o-chlorophenol at a temperature of 35° C.;

dividing the polyester resin melt into at least two portions;

passing the polyester resin melt portions through at least two passageswhich cause the intrinsic viscosity of the polyester resin melt portionsto be decreased to extents different from each other;

extruding the polyester resin melt portions which are different fromeach other, in the intrinsic viscosities thereof, through amelt-spinning orifice, in such a manner that a polyester resin meltportion having a highest intrinsic viscosity is extruded through acenter part of the orifice, and a polyester resin melt portion having alowest intrinsic viscosity is extruded through a peripheral partconcentrically surrounding the center part of the orifice, to form afilamentary stream of the polyester resin melt;

drafting and solidifying the resultant filamentary stream of thepolyester resin melt to form a monofilament of the polyester resin;

taking up the drafted and solidified polyester monofilament; and

heat-drawing the taken-up undrawn monofilament,

During the extruding step through the heat-drawing step of the processof the present invention, the polyester resin portions different inintrinsic viscosity from each other are diffused in the interfaceportion thereof, into each other, to cause thereby, the resultantmonofilament to have a distribution of the intrinsic viscosity of thepolyester resin such that the farther the location of a part of themonofilament from the longitudinal axis of the monofilament in thedirection at right angles to the longitudinal axis, the lower theintrinsic viscosity of a portion of the polyester resin located in thepart of the monofilament, and a portion of the polyester resin locatedin the peripheral part of the monofilament has an average intrinsicviscosity [η]f−p of 0.6 to 1.1 determined in o-chlorophenol at atemperature of 35° C.

In the extruding step of the process of the present invention,optionally, a polyester resin melt portion having a medium intrinsicviscosity between the highest intrinsic viscosity and the lowestintrinsic viscosity is extruded through an intermediate partconcentrically surrounding the center part and concentrically surroundedby the peripheral part of the orifice.

In the extruding step of the process of the present invention, themelt-spinning orifice may be a core-in-sheath type conjugatemelt-spinning orifice. In this case, the core-in-sheath type conjugatemelt-spinning orifice may have a sheet part composed of a peripheralpart and at least one intermediate part which are arrangedconcentrically to the core part of the melt-spinning orifice, andbetween the core part and the peripheral part of the orifice.

In the process of the present invention, the taking up step for thedrafted and solidified polyester monofilament is preferably carried outat a taking-up speed of 500 to 1500 m/min, more preferably 600 to 1300m/min. Also, in the heat-drawing step, preferably the undrawn polyestermonofilament is pre-heated to a temperature of 85 to 120° C., morepreferably 90 to 110° C. and drawn at a draw ratio of 3 to 6, morepreferably 3.5 to 5.5.

The process of the present invention will be further explained withreferring to FIGS. 3(a), 3(b) and 4.

In FIG. 3(a) showing an explanatory vertical cross-sectional view of anembodiment of the melt-spinneret usable for the process of the presentinvention, and FIG. 3(b) showing an explanatory horizontalcross-sectional view of the melt-spinneret of FIG. 3(b), along ahorizontal line A—A shown in FIG. 3(b), a melt 11 of a polyester resinis introduced into a filtering layer 13 of a melt spinneret 12 through ametering pump 14 and a conduit 15.

The filtered melt of the polyester resin is distributed into a centerhole 16 and a plurality of peripheral holes 17 formed in a distributiondisc 18. Namely, a portion of the polyester resin melt is passed througha shorter path 13 a of the filtration layer 13 and is introduced intothe center hole 16 of the distribution disc 18 and another portions ofthe polyester resin melt is passed through longer paths 13 b of thefiltration layer 13 and are introduced into a plurality of peripheralholes 17. While the melt of the polyester resin passes through thefiltering layer 13, the intrinsic viscosity of the polyester resin meltdecreases with the staying time of the polyester resin melt portion inthe filtering layer 13 and/or with the distance of the path 13 a or 13 bthrough which a portion of the polyester resin melt through in thefiltering layer 13. The portion of the polyester resin melt introducedinto the center hole 16 flows downward and is introduced into a centerpart of a funnel-shaped chamber 19 formed in an extrusion disc 20through an outlet 16 a of the center hole 16 extending downward into thefunnel shaped chamber 19. Also, the portions of the polyester resin meltintroduced into the peripheral holes 17 are introduced into a peripheralpart 21 of the funnel shaped chamber 19 through a path 22 formed betweenthe distribution disc 18 and the extrusion disc 20, and thus a compositestream consisting of a center stream formed from polyester resin meltportion having a higher intrinsic viscosity and a peripheral streamformed from the polyester resin melt portions having a lower intrinsicviscosity and concentrically surrounding the center flow is formed. Thecomposite stream flows downward through the funnel shaped chamber 19while being made thinner, and then is extruded through a melt-spinningorifice 23 to form an undrawn polyester monofilament. In the meltingstep, the dividing step and the extruding step, the polyester resin meltis kept at a temperature in the range of from 290 to 310° C.

The path length and the staying time of the portions of the polyesterresin melt, from which the peripheral part of the monofilament isformed, in the spinneret 12 are longer than those of the portion of thepolyester resin melt, from which the center part of the monofilament isformed. Thus, the intrinsic viscosity of the portion of the polyesterresin located in the peripheral part of the polyester monofilament islower than that of the portion of the polyester resin located in thecenter part of the monofilament, while these portions of the polyesterresin are formed from a single type of polyester resin. Therefore, thehigher and lower intrinsic viscosity portions of the polyester resin arecompatible with each other and diffuse into each other at the interfaceportions between the center and peripheral parts of the monofilament.Thus, a clear interface between the center and peripheral parts are notmaintained, and the intrinsic viscosity of the polyester resincontinuously changes between the center and peripheral parts of themonofilament.

For the purpose of finely controlling the difference in the intrinsicviscosity between the polyester resin portions located in the center andperipheral parts of the monofilament, intermediate holes for portions ofthe polyester resin melt may be provided between the center hole 16 andthe peripheral holes 17 so as to allow the polyester resin melt portionspassed through the intermediate holes and having a moderate intrinsicviscosity to be introduced into intermediate part between the centerpart and the peripheral part of the funnel-shaped chamber 19.

FIG. 3 shows an explanatory cross-sectional view of a melt-spinneret forproducing a polyester monofilament of the present invention having acenter part formed from a portion of a polyester resin having a highestintrinsic viscosity, an intermediate part formed from a portion of thepolyester resin having a lower intrinsic viscosity than that of thecenter part and concentrically surrounding a center part, and aperipheral part formed from a portion of the polyester resin having alowest intrinsic viscosity and concentrically surrounding theintermediate part of the monofilament.

In FIG. 3, a melt 31 of a polyester resin is fed into a melt spinneret32 through a metering pump 33 and a conduit 34. The polyester resin melt31 is distributed into three conduits 35, 36 and 37. The portion of thepolyester resin melt passed through the shorted conduit 35 is introducedinto a filtering layer 38, the filtered portion of the polyester resinmelt is introduced into a center part of a first melt chamber 39 througha conduit 40. The portion of the polyester resin melt passed through theconduit 30 which is larger than the conduit 35, is introduced into afiltering layer 41, and the filtered portion of the polyester resin meltis introduced into a peripheral part of the first melt chamber 39through a conduit 42, which is longer than the conduit 40, to provide afirst composite stream of the polyester resin in which a center streamconsisting of the portion of the polyester resin melt passed through thefiltering layer 37 is concentrically surrounded by a peripheral streamconsisting of the portion of the polyester resin melt passed through thefiltering layer 41. The first composite stream of the polyester reinmelt is introduced into a center part of a second melt chamber 43through an orifice 44 formed in a center part of the bottom of the firstmelt chamber 39 and extending downward into the second melt chamber 43.

Separately, a portion of the polyester resin melt passed through theconduit 37 which is longer than the conduit 36 was introduced into afiltering layer 45, and the filtered portion of the polyester resin meltis introduced into a peripheral part of the second melt chamber 43surrounding the center orifice of the bottom of the first melt chamber39, through a conduit 46 longer than the conduit 42. In the second meltchamber 43, the first composite stream consisting of the center streamof the portion of the polyester resin melt passed through the filteringlayer 38 and a peripheral stream of the portion of the polyester resinmelt passed through the filtering layer 41, is concentrically surroundedby a peripheral stream of the portion of the polyester resin melt passedthrough the filtering layer 45, to form a second composite stream. Inthis second composite stream, the peripheral stream of the firstcomposite stream is present as an intermediate stream concentricallysurrounding the center stream of the first composite stream andconcentrically surrounded by the peripheral stream of the secondcomposite stream.

In the spinneret 32, the portion of the polyester resin melt for thecenter stream passes through a shortest path comprising the conduit 35,the filtering layer 38 the conduit 40 and the first melt chamber and hasa highest intrinsic viscosity; the portion of the polyester resin meltfor the peripheral stream passes through a longest path comprising theconduit 37, the filtering layer 45 and the conduit 46 and has a lowestintrinsic viscosity, and the portion of the polyester resin melt for theintermediate stream passes through a middle length path comprising theconduit 36, the filtering layer 41, the conduit 42 and the first meltchamber 39, and has a moderate intrinsic viscosity.

The second composite stream flows downward through the second meltchamber while the diameter of the second composite stream iscontinuously decreased and then extruded through a melt-spinning orifice47.

The extruded monofilamentary stream is solidified while being draftedunder tension. The resultant undrawn monofilament is taken up andheat-drawn. The heat-drawing conditions are established in response tothe draft-solidifying conditions and the taking-up speed. For example,when the undrawn monofilament is taken-up at a speed of 800 to 1500m/min, it is preferably pre-heated on feed rollers at a temperature of85 to 120° C. for a preheating time of 0.5 to 1 second, and drawn at adraw ratio of 3 to 6. Optionally, the drawn polyester monofilament isheat treated at a temperature of 150 to 240° C. for 0.1 to 0.5 second.

Optionally, a plurality of undrawn polyester monofilaments are bundledand the monofilament bundle (or a multifilament yarn) is drawn andoptionally heat-treated. Then the resultant individual monofilaments areseparated from each other, if necessary. As mentioned above, since theportions of the polyester resin different in intrinsic viscosity thereoffrom each other are compatible with each other, the portions of thepolyester resin located in the core, peripheral and optionallyintermediate parts of the monofilament are easily diffused into eachother at the interface portions therebetween. Thus the interfacesbetween the parts of the monofilament are unclear.

The non-crimping polyester monofilament of the present invention can beemployed in the form of an individual monofilament, or of a doubledfilament yarn or of staple fibers, in various uses. Preferably, thepolyester monofilament of the present invention is employed in a use inwhich the monofilament is required to have a high resistance to abrasionwith metal materials. Also, the polyester monofilament of the presentinvention exhibits a high adhesive property to rubber, an excellentfatigue resistance, an enhanced dyeability of the peripheral surface ofthe monofilament, and an enhanced knot strength, and thus is useful as amaterial yarn for ropes, nets, guts, tarpaulins, tents, paragliders andsailcloths.

EXAMPLES

The present invention will be further illustrated by the followingexamples.

In the examples, intrinsic viscosity of polyester resin, and tensilestrength, ultimate elongation, yarn evenness (U %), total percentagecrimp (TC) of monofilament, evaluation of scum generation, modulus ofscreen, and general evaluation of the monofilament were determined inthe following measurements.

(1) Intrinsic Viscosity of Polyester Resin

A polyester resin was dissolved in orthochlorophenol at a temperature of35° C. in various concentration (C) to provide a plurality of dilutedsolutions. The viscosities (ηr) of the solutions were measured. Theintrinsic viscosity [η] of the polyester resin was determined inaccordance with the following equation.

[η]=limit (ln ηr/C)

(2) Tensile Strength and Ultimate Elongation

The tensile strength and ultimate elongation of a polyester monofilamentwas determined in accordance with Japanese Industrial Standard (JIS)L-1013, in which a specimen having a length of 25 cm was stretched at aelongation speed of 30 cm/min until the specimen is broken. The tensilestrength and ultimate elongation are a stress at bleak and an elongationat break of the specimen.

(3) 5% Modulus

In the measurement of the tensile strength and ultimate elongation, asmentioned above (2), a stress of the specimen generated at an elongationof 5% was measured.

(4) Yarn Evenness (U %)

A specimen of a monofilament was subjected to a yarn evennessmeasurement using an USTER 3 made of ZELLWEGER CO., at a yarn specimenlength of 300 m at a measurement rate of 100 m/minute for 3 minutes. Inthe measurement, a graph showing a relationship between the length andthe weight per length units of the specimen having a longitudinal lengthL was provided; an average weight per length units of the specimen wasdetermined from the graph; and a straight line showing the averageweight per length units of the specimen was drawn in the graph.

The U % of the specimen was calculated in accordance with the equation:${U(\%)} = {\frac{f}{F} \times 100}$

wherein F represents a total weight of the specimen having thelongitudinal length L, and f represents an integration value ofdeviations in weight from the average weight per length units of thespecimen, determined from the graph.

(5) Total Percentage Crimp (TC)

A specimen of a monofilament was reeled into a hank having a totalthickness of about 1667 dtex (about 1500 denier), a load of 19.6 N×10⁻⁶of (2 mg) was applied to a bottom center point of the hank. The loadedhank was treated in boiling water for 20 minutes and the naturally driedat 20° C. at 65% RH for one day and night, to allow the hank to crimp.The crimped monofilament hank was loaded with a load of 19.6 N×10⁻⁴ of(200 mg) per 0.9 dtex (1 denier) for one minute and then the length (l₀)of the hank was measured, the load was changed from 19.6 N×10⁻⁴ (200 mg)to 19.6 N×10⁻⁶ (2 mg) per 0.9 dtex (1 denier), was maintained for oneminute and then the length (l₁) of the hank was measured. The totalpercentage crimp (TC) was calculated in accordance with the followingequation.

TC(%)={(l ₀ −l ₁)/l ₀}×100

(6) Evaluation of Scum Generation

Polyester monofilaments were subjected to a weaving procedure forproducing a mesh weave by using a projectile type loom at a rotationrate of 250 rpm. During the weaving procedure, the staining of the reedsis observed, and when the reed is stained to such an extent that theweaving procedure cannot be continued, the weaving procedure isinterrupted to clear the reed. The length of the resultant mesh fabricobtained between the start and the interruption of the weaving procedureis referred to a reed-cleaning period (m). The longer the reed-cleaningperiod, the smaller the amount of scum generated on the reed.

(7) Modulus of Monofilament Screen Weave

A specimen of monofilament screen weave (plain guaze) having a width of5 cm was subjected to a tensile test at a length of the specimen betweengripping members at a tensile rate of 10 cm/min, using a constant ratestretch type tensile tester in accordance with JIS L1096, to prepare astress-strain curve of the screen weave. When the elongation of thespecimen reaches 10%, the tensile stress (N (kgf)) is measured. Themodulus of the screen weave is represented by the tensile stress at anelongation of 10%.

(8) General Evaluation

From the evaluation result of scum generation and the screen weavemodulus, the monofilament is evaluated in the following three classes.

Class Reed-cleaning period (m) Screen weave modulus (N) 3 250 m or more140.1N (15 kgf) or more 2 100 m or more 98.1N (10 kgf) or more but lessthan 250 m but less than 140.1N (15 kgf) 1 Less than 100 m Less than98.1N (10 kgf)

Reference Example 1

A polyester (polyethylene terephthalate) resin was subjected to heattreatments in a nitrogen gas atmosphere (no oxygen atmosphere) at thetemperature of 280 to 300° C. for the times of 5 to 15 minutes shown inTable 1, and each heated specimen was subjected to a intrinsic viscositymeasurement. The resultant reduction in intrinsic viscosity in each heattreatment is shown in Table 1.

TABLE 1 Heating temperature Heating time 280° C. 290° C. 300° C.  5minutes 0.016 0.031 0.049 10 minutes 0.031 0.050 0.087 15 minutes 0.0460.065 0.112

Table 1 shows that the higher the heating temperature and the longer theheating time, the longer the reduction in the intrinsic viscosity of thepolyester resin. Namely, the intrinsic viscosity reduction by theheating treatment at a temperature of 300° C. for 10 minutes is largerby 0.071 than that by the heating treatment at a temperature of 280° C.for 5 minutes.

When the heat-treated polyester resin at 300° C. for 10 minutes ismelt-spun at an extruding rate of 4.27 g/minute at a taking up speed of1200 m/minute and the resultant undrawn filament is drawn at a drawratio of 3.8, the resultant drawn filaments had an ultimate elongationof about 12% higher than that of the drawn polyester filaments producedfrom the heat-treated polyester resin at a temperature of 280° C. for 5minutes through the same procedures as mentioned above.

To obtain a large difference in the intrinsic viscosity of the polyesterresin generated due to difference in heat history during the undrawnmonofilament-forming procedures, the starting polyester resin preferablyhas a relatively high average intrinsic viscosity ([η]f−a), for example,of 0.65 or more, more preferably 0.70 or more, but usually not more thanabout 1.3.

To generate the difference in the intrinsic viscosity of the polyesterresin, a plurality of melt-extruders having extruding temperaturesdifferent from each other may be employed. In this case, the center,peripheral, and optionally intermediate parts of the monofilament areformed from a plurality of polyester resin melts different intemperature from each other and supplied from the plurality ofextruders. This monofilament-producing process is similar to that forproducing composite monofilament from a plurality of polymers differentin type thereof, and is disadvantageous in that the employment of theplurality of extruders causes the production cost of the monofilament tobe very high and the production of very thin monofilament to becomedifficult.

In another process, a plurality of monofilaments can be produced by amelt-spinning procedure using only one metering pump, and are thenseparated from each other. In this method, the proportion of the sheathpart of the monofilament can be easily made small. However, in thisprocess including the monofilament-separating procedure, it is difficultto severely uniformalize the thickness of the separated monofilaments.

Reference Example 2

A polyethylene trephthalate resin having an intrinsic viscosity [η] of0.90 was melted in a melt-extruder and the melting temperature of theresin was controlled to 290° C. The melt is passed through a heating boxheated with a heating medium to a temperature of 300° C. and thenextruded through a metering gear pump with 0.3 ml/rev. The measuredtemperature of the extruded melt through the metering pump was 300° C.In the above-mentioned melting and gear pump extruding procedures forthe melt, the gear pump extruding rate was varied as shown in Table 2,and the extruded melt samples were subjected to the intrinsic viscositymeasurement. The measurement results are shown in Table 2.

TABLE 2 Run Gear pump extrusion Intrinsic viscosity of No. rate 1g/minute extruded melt samples 1 5.0 0.78 2 7.5 0.80 3 10.0 0.82 4 12.50.83

Table 2 shows that the higher the gear pump extrusion rate, and thus theshorter the staying time of the melt in the gear pump, the higher theintrinsic viscosity of the extruded melt, and thus the smaller areduction in the intrinsic viscosity of the extruded melt. The absolutevalue of the intrinsic viscosity reduction is variable in response tothe volume of path for the melt in the melt-spinning apparatus andtemperature profile of the melt. When a single and the same apparatus isemployed, the reduction in the intrinsic viscosity of the polyesterresin melt is effected in response to the heating temperature and theheating time applied to the melt.

Separately, the same heating and extruding procedures as mentioned abovewere carried out except that the gear pump extrusion rate was fixed to7.5 g/minute, the melt was passed through a filtering layer having thefiltering volume (internal volume) as shown in Table 3, and afterstaying in the extruder apparatus for the average time as shown in Table3, the filtered melt was extruded. The extruded melt was subjected tothe intrinsic viscosity measurement. The measurement results are shownin Table 3.

TABLE 3 Volume of Staying time of Intrinsic viscosity Run filtering meltof extruded melt No. layer (ml) (minute) ([η]f) 1 12 2 0.780 2 24 40.761 3 60 10 0.711

Table 3 shows that the intrinsic viscosity of the polyester resin meltdecreases with an increase in the staying time of the melt.

EXAMPLE 1

A polyethylene terephthalate resin having an intrinsic viscosity of 0.8was melted at a temperature of 300° C. and fed into a melt spinneret asshown in FIGS. 3(a) and 3(b) through a metering gear pump 14 at a feedrate of 5 ml/minute. In the melt spinneret 12 of FIGS. 3(a) and 3(b) hada total inner volume of 12 ml, the distribution disc 18 had a centerpath 16 having a diameter of 5 mm, and 24 peripheral paths 17 arrangedon a circle concentric to the center path 16. The peripheral paths hadthe diameter as shown in Table 4. The composite stream formed in themelt chamber 19 was extruded through the melt-spinning orifice 23 at anextrusion rate of 5 ml/minute. The extruded monofilamentary streampassed through a heating atmosphere zone having a temperature of 350° C.and a length of 100 mm, then cool-solidified under drafting and taken upat a speed of 1000 m/minute. The resultant undrawn monofilament wasbrought into contact with drawing hot rolls heated respectively at atemperature of 100° C. and 140° C. and drawn at a draw ratio of 4.0between the drawing rolls. A polyester monofilament having a thicknessof 10 dtex (9 denier) was obtained.

The drawn monofilament was subjected to a measurement of averageintrinsic viscosity thereof and thereafter to a mild alkali weightreduction treatment in an aqueous sodium hydroxide (NaOH) solutionhaving a two mole (2 M) concentration and containing 3 g/liter of anquaternary ammonium salt type alkali weight reduction promotor, in aliquor ratio (a ratio in weight of the treating bath to themonofilament) of 200 or more at a temperature of 30° C. When thethickness of the monofilament reached to 8.9 dtex (8 denier), themonofilament was washed with water, dried in the ambient air atmosphereand subjected to an average intrinsic viscosity measurement. Theseprocedures were repleated when the thickness of the monofilament wasreduced to 7.8 dtex (7 denier), to 6.7 dtex (6 denier), and 5.6 dtex (5denier). From the resultant data, average intrinsic viscosities of thecenter part having a thickness of 5.6 dtex (5 denier), a first annularpart having an inner thickness of 5.6 dtex (5 denier) and an outerthickness of 6.7 dtex (6 denier) and surrounding the center part, asecond annular part surrounding the first annular part and having aninner thickness of 6.7 dtex (6 denier) and an outer thickness of 7.8dtex (7 denier), a third annular part surrounding the second annularpart and having an inner thickness of 7.8 dtex (7 denier) and an outerthickness of 8.9 dtex (8 denier), and an outermost is annular partsurrounding the third annular part and having an inner thickness of 8.9dtex (8 denier) and an outer thickness of 10 dtex (9 denier), werecalculated. The results are shown in Table 4. In the calculation, when apolymer having an intrinsic viscosity of 0.8 was mixed with anotherpolymer having an intrinsic viscosity of 0.75 in a weight ratio of 1:1,the mixed polymer has an average intrinsic viscosity of{(0.8×1)+(0.75×1)}/(1+1)=0.775.

Comparative Example 1

A polyester monofilament was prepared and tested by the same proceduresas in Example 1, except that the filtration of the polyester resin meltwas carried out so that no difference in intrinsic viscosity wasgenerated between the portion of the melt for forming the center portionand the portions of the melt for forming the peripheral portion of themonofilament. For this purpose, in the melt spinneret as shown in FIGS.3(a) and 3(b), all the peripheral holes 17 are closed and five staticmixers were arranged in series in the center hole 16, so that thepolyester resin melt can uniformly pass through the filtering layer 13without generating a difference in staying time between portions of thepolyester resin melt.

The test results are shown in Table 4.

TABLE 4 Item Average intrinsic viscosity [η] f-a Center part Peripheralpart Diameter of with Thickness Thickness Thickness Thickness peripheralthickness 5.6 to 6.7 to 7.8 to 8.9 to Example No. hole 17 (mm) of 5.6dtex 6.7 dtex 7.8 dtex 8.9 dtex 10 dtex Example 1 Run 1 3 0.754 0.7510.747 0.743 0.738 Run 2 1.5 0.762 0.754 0.745 0.732 0.724 Run 3 1.00.765 0.759 0.740 0.705 0.689 Comparative — 0.744 0.743 0.746 0.7440.745 Example 1

Table 4 clearly shows that when the flow rate of the portion of thepolyester melt through the peripheral holes 17 is restricted (made low),the reduction in intrinsic viscosity of the portion of the polyesterresin melt could be larger than that of the portion of the polyesterresin melt passed through the center hole 16.

In the comparative Example 1, substantially no difference in intrinsicviscosity of the polyester resin was generated between the center partand the peripheral part of the monofilament.

EXAMPLE 2 and 3

and

Comparative Examples 2 and 3

In each of Examples 2 and 3 and Comparative Examples 2 and 3, apolyester monofilament having a thickness of 10 dtex (9 denier) wasprepared and tested by the same procedure as in Example 1, Run 2, exceptthat the extrusion rate was 5 g/minute and the taking up speed and drawratio were controlled to provide a monofilament having the tensilestrength and the ultimate elongation as shown in Table 5. In thecomparative Examples 2 and 3, a usual simple melt spinneret formonofilament was employed.

The monofilament was converted to a 350 mesh screen weave by using aprojectile type loom under a warp tension of 98.0655 mN (10 gf) permonofilament at a reed clearance of 35 μm and finished.

The physical properties and weaving property of the monofilament and theevaluation results of the screen weave are shown in Table 5.

TABLE 5 Item Monofilament Screen weave Tensile Ultimate Tensile stressScum Modu- General Type of strength elongation at 5% elonga- genera- lusevalu- Example No. spinneret (N/1.1 dtex) (%) tion (N) tion (m) (N)ation Example 2 FIGS. 3(a) 6.7 41 26.5 600 98.1 2-1 3 and 3(b) 7.2 3138.2 280 186.3 3 Comparative Example 2 Simple 6.7 40 26.5 240 88.3 2-1 3spinneret 7.2 30 39.2  50 176.5 1

Table 5 shows that when the polyester monofilaments of the presentinvention are useful for producing screen weave having a high modulusfor screen printing and exhibit a high resistance to scum generationduring the weaving procedure.

Industrial Applicability

In the polyester monofilament of the present invention has a center partformed from a portion of a polyester resin having a high intrinsicviscosity, and a peripheral part formed from another portion of thepolyester resin having a low intrinsic viscosity. In the intrinsicviscosity distribution of the monofilament, the intrinsic viscositydecreases with increase in the distance from the longitudinal axis ofthe monofilament. The polyester monofilament of the present inventioncan be produced by the process of the present invention wherein, in amelt spinneret, a portion of the polyester resin melt supplied into thespinneret is caused to have a higher reduction in the intrinsicviscosity than that of another portion of the polyester resin melt, anda peripheral part of the monofilament is formed from the portion of thepolyester resin melt having a lowest intrinsic viscosity and a centerpart of the monofilament is formed from another portion of the polyesterresin melt.

The difference in reduction of the intrinsic viscosity can be controlledby controlling the heat history (staying time and heating temperature)of each portion of the polyester melt in the spinneret.

When the polyester monofilament of the present invention is employed toproduce a screen weave (plain gauze), the polyester monofilament of thepresent invention having, as a whole, a high tensile strength, a highmodulus and a low ultimate elongation enables the generation of scumduring the weaving procedure to prevent or restrict. Also, the polyestermonofilament of the present invention can have a smaller thickness thanthat of conventional polyester monofilaments. Thus, the polyestermonofilament of the present invention enables various mesh woven fabricshaving a high modulus, high warp and weft densities, a high ratio oftotal opening area to the total area of the fabric, and a highmechanical strength to be practically produced. Also, when the meshwoven fabrics are employed for screen printing, the accuracy of theprinting is high, the resistance to fatigue of the fabric due to asqueezing action applied to the fabric during printing procedure ishigh, and an elongation of the fabric during the printing procedure islow.

Thus, the polyester monofilament and the polyestermonofilament-producing process of the present invention can beadvantageously employed in practice.

What is claimed is:
 1. A non-crimping polyester monofilament formed froma polyester resin, wherein the polyester resin has an intrinsicviscosity which varies in such manner that the farther the location of apart of the monofilament from the longitudinal axis of the monofilamentin the direction at right angles to the longitudinal axis, the lower theintrinsic viscosity of a portion of the polyester resin located in thepart of the monofilament, and a portion of the polyester resin locatedin a peripheral part (p) of the monofilament has an average intrinsicviscosity [η]f−p of 0.6 to 1.1, determined in orthochlorophenol at atemperature of 35° C., the peripheral part (p) concentricallysurrounding a center part (c) of the monofilament extending along thelongitudinal axis of the monofilament.
 2. The polyester monofilament asclaimed in claim 1, wherein the center part (c) extending along alongitudinal axis of the monofilament has a high average intrinsicviscosity and is concentrically surrounded by the peripheral part (p) ofthe monofilament.
 3. The polyester monofilament as claimed in claim 1,wherein the center part (c) extending along a longitudinal axis of themonofilament has a high average intrinsic viscosity and isconcentrically surrounded by an intermediate part (i) and the peripheralpart (p) of the monofilament concentrically surrounds the intermediatepart (i) of the monofilament, the portion of the polyester resin locatedin the intermediate portion of the monofilament having an intrinsicviscosity lower than that of the center part (c) but higher than that ofthe peripheral part (p).
 4. The polyester monofilament as claimed inclaim 1, wherein the polyester resin comprises a single chemical type ofa polyester polymer.
 5. The polyester monofilament as claimed in claim1, wherein the polyester resin comprises at least one member selectedfrom the group consisting of polyethylene terephthalate, polybutyleneterephthalate, polyethylene naphthalate, and polytrimethyleneterephthalate.
 6. The polyester monofilament as claimed in claim 1,wherein the polyester resin for the polyester monofilament has anaverage intrinsic viscosity [η]f−a of 0.7 to 1.2, determined asmentioned above.
 7. The polyester monofilament as claimed in claim 1,wherein a portion of the polyester resin located in the center part (c)of the monofilament has an average intrinsic viscosity [η]f−c of 0.7 to1.3, determined as mentioned above, which is higher than the averageintrinsic viscosity [η]f−p of the portion of the polyester resin locatedin the peripheral part of the monofilament.
 8. The polyestermonofilament as claimed in claim 1, wherein the average intrinsicviscosity [η]f−p of the portion of the polyester resin located in theperipheral part of the monofilament is in the range of from 0.6 to 1.0,determined as mentioned above.
 9. The polyester monofilament as claimedin claim 1, wherein the average intrinsic viscosity [η]f−c of theportion of the polyester resin located in the center part (c) of themonofilament is 0.02 to 0.20 above the average intrinsic viscosity[η]f−p of the portion of the polyester resin located in the peripheralpart (p) of the monofilament.
 10. The polyester monofilament as claimedin claim 1, wherein in the cross-section of the monofilament, the areaof the center part (c) of the monofilament is in a proportion of 0.6 to0.95 to the whole cross-sectional area of the monofilament.
 11. Thepolyester monofilament as claimed in claim 1, wherein in thecross-section of the monofilament, the area of the peripheral part (p)of the monofilament is in a proportion of 0.05 to 0.4 to the wholecross-sectional area of the monofilament.
 12. The polyester monofilamentas claimed in claim 1, wherein the cross-sectional profile of themonofilament is in the form of a circle.
 13. The polyester monofilamentas claimed in claim 12, wherein in the circular cross-section of themonofilament, a ratio Lc/R of the thickness Lc of the center part (c) ofthe monofilament to the radius R of the monofilament is in the range offrom 0.77 to 0.98.
 14. The polyester monofilament as claimed in claim12, wherein in the circular cross-section of the monofilament, a ratioLp/R of the thickness Lp of the peripheral part (p) of the monofilamentto the radius R of the monofilament is in the range of from 0.02 to0.23.
 15. The polyester monofilament as claimed in claim 1, wherein thepolyester resin from which the monofilament is constituted has anaverage gradient (α) of intrinsic viscosity thereof in a range of from 1to
 30. 16. The polyester monofilament as claimed in claim 1, having anaverage tensile strength of 52.96 to 88.26 mN/dtex (6.0 g/d to 10.0g/d).
 17. The polyester monofilament as claimed in claim 1, exhibiting astress of 26.48 mN/dtex(3.0 g/d) or more under an elongation of 5%thereof.
 18. The polyester monofilament as claimed in claim 1, having anaverage ultimate elongation in a range of from 10 to 30%.
 19. Thepolyester monofilament as claimed in claim 1, having an evenness(U%) inthickness thereof of 1.5% or less.
 20. The polyester monofilament asclaimed in claim 1, having a thickness of 2.2 to 55.6 dtex (2 to 50denier).
 21. A process for producing a non-crimping polyestermonofilament, comprising: melting a polyester resin having an intrinsicviscosity of 0.8 to 1.3, determined in o-chlorophenol at a temperatureof 35° C.; dividing the polyester resin melt into at least two portions;passing the polyester resin melt portions through at least two passageswhich cause the intrinsic viscosity of the polyester resin melt portionsto be decreased to extents different from each other; extruding thepolyester resin melt portions, which are different from each other inthe intrinsic viscosities thereof, through a melt-spinning orifice insuch a manner that a polyester resin melt portion having a highestintrinsic viscosity is extruded through a center part of the orifice,and a polyester resin melt portion having a lowest intrinsic viscosityis extruded through a peripheral part concentrically surrounding thecenter part of the orifice, to form a filamentary stream of thepolyester resin melt; drafting and solidifying the resultant filamentarystream of the polyester resin melt to form a monofilament of thepolyester resin; taking up the drafted and solidified polyestermonofilament; and heat-drawing the taken-up undrawn monofilament,wherein during the extruding step through the heat-drawing step, thepolyester resin portions different in intrinsic viscosity from eachother are diffused, in the interface portion thereof, into each other,to cause the resultant monofilament to have a distribution of theintrinsic viscosity of the polyester resin such that the farther thelocation of a part of the monofilament from the longitudinal axis of themonofilament in the direction at right angles to the longitudinal axis,the lower the intrinsic viscosity of a portion of the polyester resinlocated in the part of the monofilament, and a portion of the polyesterresin located in the peripheral part of the monofilament has an averageintrinsic viscosity [η]f−p of 0.6 to 1.1 determined in o-chlorophenol ata temperature of 35° C.
 22. The process for producing a non-crimpingpolyester monofilament as claimed in claim 21, wherein in the extrudingstep, a polyester resin melt portion having a medium intrinsic viscositybetween the highest intrinsic viscosity and the lowest intrinsicviscosity is extruded through an intermediate part concentricallysurrounding the center part and concentrically surrounded by theperipheral part of the orifice.
 23. The process for producing anon-crimping polyester monofilament as claimed in claim 21, wherein themelt-spinning orifice is a core-in-sheath type conjugate melt-spinningorifice.
 24. The process for producing a non-crimping polyestermonofilament as claimed in claim 23, wherein the melt-spinning orificeis a core-in-sheath type conjugate melt-spinning orifice in which thesheath part is composed of a peripheral part and at least oneintermediate part which are arranged concentrically to the core part ofthe melt-spinning orifice.
 25. The process for producing a non-crimpingpolyester monofilament as claimed in claim 21, wherein the polyesterresin comprises a single chemical type of polyester polymer.
 26. Theprocess for producing a non-crimping polyester monofilament as claimedin claim 21, wherein the polyester resin comprises at least one memberselected from the group consisting of polyethylene terephthalate,polybutylene terephthalate, polyethylene naphthalate andpolytrimethylene terephthalate.
 27. The process for producing anon-crimping polyester monofilament as claimed in claim 21, wherein thetaking up step for the drafted and solidified polyester monofilament iscarried out at a taking-up speed of 500 to 1500 m/min.
 28. The processfor producing a non-crimping polyester monofilament as claimed in claim21, wherein in the heat-drawing step, the undrawn polyester monofilamentis pre-heated to a temperature of 85 to 120° C. and drawn at a drawratio of 3 to 6.